Linear Compressor with Carbon Fibre Reinforced Spring

ABSTRACT

A linear compressor having a piston housing and a compressor piston configured for reciprocating movement therein along an axis, the linear compressor having means for guiding the compressor piston in a direction generally perpendicular to the axis and means for buffering kinetic energy associated with the reciprocating movement of the compressor piston. The linear compressor includes an elastic element made from composite material operatively associated with at least one of the means for guiding and the means for buffering.

The invention relates to a linear compressor, comprising a piston housing and a compressor piston moving back and forth therein along an axis, comprising a means for guiding the compressor piston in a direction that is perpendicular to the axis and a means for buffering the kinetic energy of the back and forth movement of the compressor piston; a refrigerating device, in particular a refrigerator and/or a freezer or an air conditioning unit; as well as a method for cooling goods and a method for compressing a fluid.

In the case of a linear compressor, the compressor piston moving back and forth along an axis between a first reversal point and a second reversal point must be supported or guided in a direction that is perpendicular to the axis. Over and above that, the kinetic energy of the compressor piston moving back and forth must be buffered at the reversal points, i.e. at the points where the direction of movement of the compressor piston is reversed in order to make possible a reversal in the direction of movement of the compressor piston with the lowest loss possible. By way of the reversal in the direction of movement, the compressor piston carries out an oscillating, in essence translatory back and forth movement in a piston housing. By means of the back and forth movement, a process of compression is carried out.

It is well known to support the moving parts, in particular the compressor piston, in contact with or by means of a gas thrust bearing. In the case of these systems, one coil spring or a plurality of coil springs are usually used for buffering the kinetic energy of the moving parts. Systems with an open type of construction, i.e. a motor-driven pump arranged in series, use a set of springs of one or more very thin diaphragm springs or sets of diaphragm springs and one or more coil springs or sets of coil springs to support the compressor piston in a radial direction, i.e. perpendicular to the axis, and store the kinetic energy. Such springs are made of metal, in particular spring steel. In this process, the diaphragm springs are made so thin and soft that the total of the transverse rigidities of the springs can sufficiently absorb the forces developing vertical to the direction of oscillation of the entire system. In order to achieve an optimal longitudinal rigidity, spring arrangements are well known in which diaphragm springs are supported by one or more coil springs or sets of coil springs.

It is an object of the present invention to provide a linear compressor or a refrigerating device in which a back and forth movement of a compressor piston being used can be carried out reliably during compression and while saving energy in a simple manner.

In addition, it is an object of the invention to provide a method for compressing a fluid as well as a method for cooling goods, it being possible that a process of compression or a process of cooling can be carried out with a high degree of reliability and while saving energy in particular.

This object is achieved in accordance with the invention by means of the linear compressor and by means of the refrigerating device as well as by means of the method for the compression of a gas and by means of the method for cooling goods as specified in the independent claims. Further advantageous embodiments and developments, which can be used individually or randomly combined with one another in each case, form the subject matter of the respective dependent claims.

The linear compressor in accordance with the invention comprises a piston housing and a compressor piston moving back and forth therein along an axis, comprising a means for guiding the compressor piston in a direction that is perpendicular to the axis and a means for buffering the kinetic energy of the back and forth movement of the compressor piston, it being possible that the means for guiding and/or the means for buffering has an elastic element made from composite material.

By using a composite material, the structure of the linear compressor can be simplified considerably and the operation of the linear compressor can be more reliable, energy saving and efficient.

The compressor piston can be supported without oil in the piston housing, for example supported by means of a gas thrust bearing.

By using the means for guiding, the compressor piston is guided in such a way in a housing in a direction that is perpendicular to the axis that the friction between the compressor piston and the piston housing is as low as possible in order to keep the wear of the compressor piston or piston housing low. The means for guiding thus guides the compressor piston in a radial direction and prevents the compressor piston from jamming in the piston housing. Excessive friction of the compressor piston against the walls of the housing or an uncontrolled striking against said walls is prevented in this way.

With the aid of the means for buffering the kinetic energy of the compressor piston moving back and forth, the kinetic energy of the parts moving back and forth in the linear compressor, in particular of the compressor piston, is temporarily absorbed, it being possible that the moving parts are slowed down during their backward movement shortly before a reversal point and accelerated during their forward movement shortly after the reversal point.

The means for buffering is able to absorb at least the kinetic energy of the moving parts that the moving parts can absorb in the case of a backward and forward movement. In this instance, in particular the kinetic energy over a section of at least 5%, preferably at least 10%, for example over a section of 30% of the total stroke of the compressor piston is converted into potential energy, which is for example caused by means of the compression of a spring. With the help of the means for buffering, the moving parts can move back and forth in an oscillating manner. In this way, the means for buffering forms part of an oscillating system. The oscillating system can be regarded approximately as a harmonic oscillator by means of which an oscillatory process of compression can be carried out. With the means for buffering, at least 85%, in particular at least 95%, preferably at least 98%, in essence in a particularly preferred manner 100% of the kinetic energy of the compressor piston can be absorbed before a reversal point, and can subsequently again be released to the compressor piston.

The means for buffering the kinetic energy is formed by means of an elastic element, in particular a spring, preferably a diaphragm spring, made from composite material. By means of this selection, in comparison with the prior art considerable simplifications of the type of construction of the linear compressor are possible. Over and above that, the operation of the linear compressor can be simplified and designed to be more energy-efficient for this reason. In addition, the linear compressor can be constructed to be more compact and lighter, which in particular offers additional application possibilities of the linear compressor, in particular for mobile applications.

A composite material is a construction material consisting of 2 or more different materials such as for example fibers, plastic, metal, and ceramics. At least one component, such as for example fibers, is embedded in the basic structure, a so-called matrix. In this process, an attempt will be made to combine the different advantages of the individual materials into the end material and to exclude their disadvantages. As composite material, carbon fiber reinforced plastic (CFP), glass fiber reinforced plastic (GfP), TiGr composite, i.e. a compound of titanium, graphite and epoxy resin, and others can be used.

With the help of the composite material, a spring constant of the elastic element can be predefined in an accurate manner. Simply because it is possible to customize the properties of the composite material, the spring properties may be influenced positively, especially depending on the direction.

In particular, the ratio of the axial rigidity to the transverse rigidity can also be predefined and customized. In this case, the highest possible transverse rigidities are aimed for in order to bring about a movement of the moving parts that is as lacking in design as possible, in particular of the compressor piston in a direction that is perpendicular to the axis. The axial rigidity of the elastic element along the axis must be dimensioned in such a way that the kinetic energy of the moving parts can be absorbed completely. The ratio of the axial rigidity to the transverse rigidity ranges in particular from 1:20 to 1:200, in particular from 1:40 to 1:100.

By using a composite material, a spring element can be manufactured, which combines the properties of all the different spring elements of a linear compressor. The spring element can have both the function of a lateral guiding of the moving parts in the linear compressor and the function of buffering the kinetic energy during a reversal in the direction of movement. As a result of this, the structure of the linear compressor is clearly simplified and the number of parts, the costs, and the assembly complexity considerably reduced. In addition to the low total costs of the linear compressor, the outer dimensions as well as the weight are also considerably reduced in this way.

The elastic element is fiber reinforced in an advantageous manner, it being possible to use in particular carbon fibers, glass fibers, and/or aramid fibers. Aramid fibers, which are sold under the brand name Kevlar, are fibers made from aromatic polyamides, it being possible to differentiate between meta-aramids as well as para-aramids. Polyamides with aromatic groups in the main chain are not per se called aramids or aromatic polyamides (poly-aramids), but, according to a definition of the US Federal Trade Commission, only those long-chain synthetic polyamides in which at least 85% of the amide groups are bound directly to 2 aromatic rings. Polyphenylene terephthalamide can for example be used.

In addition, the elastic element can contain a plastic, in particular a polymer, such as for example a synthetic resin or an epoxy resin.

To this end, the elastic element is suitable for storing and again releasing the kinetic energy of the compressor piston moving back and forth in an advantageous manner. In this case it is advantageous if the elastic element in essence can completely absorb the kinetic energy of the parts moving back and forth, but it is also possible to develop a smaller absorption capacity for the spring and to absorb a part of the kinetic energy by means of another elastic element associated with the compressor piston or by means of a drive. In the latter case, a part of the kinetic energy of the compressor piston can be buffered electrically, for example with the help of a condenser and/or a coil.

The elastic element again releases the largest part of the energy stored by it, in particular at least 80%, in particular at least 90%, preferably at least 98%. By means of an inner absorbability of the elastic element that is as low as possible, an improved degree of efficiency of the linear compressor is achieved.

In an advantageous embodiment of the invention, the compressor piston can be guided by means of the elastic element, in particular by way of the spring, in a direction that is perpendicular to the axis.

This means that the elastic element fulfils two functions, namely, on the one hand, it provides guidance in a radial direction, and on the other hand it forms an energy store. The means for guiding the compressor piston in a direction that is perpendicular to the axis and the means for buffering the kinetic energy of the compressor piston moving back and forth are in this way implemented with the same component. As a result of this, the design of the linear compressor is simplified considerably.

The mass of the compressor piston moving back and forth may lie between 20 and 200 g, in particular between 40 and 60 g. The compressor piston is operated in the piston housing at a frequency ranging from 20 Hz to 200 Hz, in particular between 40 Hz and 60 Hz. In this case, the frequency of the back and forth movement is selected corresponding to the resonance maximum occurring during the operation of the linear compressor. In this process, the moving parts and the means for buffering form an oscillating system, which is coupled to the fluid and which has its characteristic frequencies with corresponding resonance curves. The working frequency of the linear compressor lies in the vicinity of a resonance frequency in an advantageous manner. In such a resonance, the degree of efficiency of the linear compressor is particularly high. The compressor piston can be guided in the piston housing with the help of a housing wall having at least one opening and a fluid flowing through said opening, in particular a means for cooling. By way of the flowing, gaseous fluid, a gas cushion is created between the piston housing and the wall of the housing, which makes possible a contact-free guidance of the compressor piston in the piston housing. In principle, the principle of gas compression retention can also be applied to liquid fluids.

In a special embodiment of the invention, the elastic element has a spring constant ranging from 2000 kg/s² to 20000 kg/s², in particular between 3000 kg/s² and 6000 kg/s². Such spring constants are advantageous for linear compressors to be used in refrigerators and/or freezers or in an air conditioning unit, in particular in an air conditioning unit for motor vehicles.

The ratio of the axial rigidity to the transverse rigidity of the elastic element is at least 1:20, in particular at least 1:50, preferably at least 1:100. The elastic element is very soft in a direction parallel to the axis, so that the compressor piston can perform a stroke over a section ranging from 5 mm to 50 mm, in particular between 10 mm and 30 mm. Because of the high transverse rigidity of the element, the lateral movement of the compressor piston in a direction that is perpendicular to the axis is very limited and is in particular less than 0.2 mm, in particular less than 0.1 mm, preferably less than 0.05 mm. As a result of this, an accurate lateral guidance of the compressor piston is carried out whereby the friction between the compressor piston and the piston housing is sufficiently limited so that an excessive wear of the linear compressor is prevented.

The elastic element forms both the means for guidance and the means for buffering in an advantageous manner. In this way, the elastic element has a double function, which is advantageous in the light of a method of the construction of the linear compressor, the design of which is as simple as possible.

The refrigerating device in accordance with the invention, in particular a refrigerator and/or a freezer or an air conditioning unit, in particular an air conditioning unit for motor vehicles, comprises the linear compressor in accordance with the invention. Because of the simple method of the construction of the linear compressor in accordance with the invention, the refrigerating device can be manufactured in a simpler and more cost-effective manner. By using a composite material, the structure of the linear compressor and for this reason also of the refrigerating device can be structured simply and the refrigerating device can be operated in a reliable, energy saving and efficient manner.

The method for cooling goods in accordance with the invention uses the refrigerating device in accordance with the invention and/or the linear compressor in accordance with the invention and the method for compressing a fluid in accordance with the invention uses the linear compressor in accordance with the invention. By using the refrigerating device in accordance with the invention and/or the linear compressor in accordance with the invention, a particularly reliable, energy saving and rapid cooling of goods or compression of fluids is made possible.

Further advantages and particular developments of the invention are described in more detail with reference to the following drawings, which do not impose limits on the invention but are only exemplary illustrations. The following is shown schematically:

FIG. 1 shows a known linear compressor in perspective view,

FIG. 2 shows a linear compressor in accordance with the invention in perspective view;

FIG. 3 shows a refrigerating device in accordance with the invention, and

FIG. 4 shows a section of a further linear compressor in accordance with the invention in a sectional view.

FIG. 1 shows a known linear compressor 1 in perspective view with a drive 13, which is connected to a piston housing 2 of the linear compressor 1 by means of a coupling rod 14. A compressor piston (not shown) moves back and forth in a piston housing 2. In the case of a reversal in the direction of movement, the kinetic energy of the compressor piston or of the parts moving back and forth is absorbed by means of cylinder springs 16 and diaphragm springs 15. The compressor piston moves back and forth along an axis 3.

FIG. 2 shows a linear compressor 1 in accordance with the invention in perspective view with a drive 13, which is connected to a compressor piston 4 by means of a coupling rod 14 (see FIG. 4). Piston 4 is slowed down or accelerated with the help of an elastic element 7, which is embodied as a spring 8 reinforced with carbon fiber, guided both in a direction that is perpendicular to an axis 3 and in a direction along the axis 3. The spring 8 temporarily absorbs the kinetic energy of the compressor piston 4 and again releases it to the latter after the reversal in the direction of movement.

FIG. 3 shows a refrigerating device 17 in accordance with the invention, which is embodied as a refrigerator and has the linear compressor 1 in accordance with the invention in order to cool down or to keep cool the goods 18 as quickly, energy-efficiently and reliably as possible.

FIG. 4 shows a sectional view of a further linear compressor 1 in accordance with the invention, in the case of which a compressor piston 4 moves back and forth along an axis 3 with the help of a drive 13. The compressor piston 4 is supported in a piston housing 2 with the help of a housing wall 11 having openings 10, it being possible that a gaseous fluid 21 is squeezed from a supply line 20 through the openings 10 towards the compressor piston 4 so that the compressor piston 4 is supported contact-free by means of the gas cushion 19 produced hereby in front of the housing wall 11. Over and above that, the compressor piston 4 is guided by means of a high transverse rigidity of the elastic element 7 in a direction 22 that is perpendicular to the axis 3. The elastic element 7 is a spring which is reinforced with carbon fibers. The spring 8, which with its ends, on the one hand, is secured to the piston housing 2, and on the other hand to a coupling rod 14 connecting the drive 13 to the compressor piston 4, in essence, completely absorbs the kinetic energy of the compressor piston 4 so that for this reason the compressor piston 4 changes its direction of movement along the axis 3. Over and above that, the spring 8 is also used to support the compressor piston 4 in a direction that is perpendicular to the axis 3. For this reason, the spring 8 has a double function and, on the one hand, brings about a lateral support of the compressor piston 4, and on the other hand a buffering of the kinetic energy of the compressor piston 4 in the form of potential energy in order to facilitate a reversal in the direction of movement. As a result of this double function, no other guiding elements, such as for example a second diaphragm spring, the cylinder springs or further couplings, are used.

The invention relates to a linear compressor 1, comprising a piston housing 2 and a compressor piston 4 moving back and forth therein along an axis 3, comprising a means 5 for guiding the compressor piston 4 in a direction that is perpendicular to the axis 3 and a means 6 for buffering the kinetic energy of the back and forth movement of the compressor piston 4 for a reversal in the direction of movement of the compressor piston 4, it being possible that the means 5 for guiding and/or the means 6 for buffering has an elastic element 7 made from composite material, in particular formed by means of a spring 8 reinforced with carbon fiber; a refrigerating device 17, such as for example, a refrigerator, comprising the linear compressor 1 in accordance with the invention; and a method for compression of a fluid and a method for cooling goods 18. The invention permits the construction of a linear compressor 1 or refrigerating device 17 of simple design and provides an energy saving, efficient and reliable operational method for cooling goods 18 or compressing a fluid.

LIST OF REFERENCE CHARACTERS

-   -   1 Linear compressor     -   2 Piston housing     -   3 Axis     -   4 Compressor piston     -   5 Means for guiding the compressor piston 4     -   6 Means for buffering the kinetic energy of the back and forth         movement of the compressor piston 4     -   7 Elastic element     -   8 Spring     -   9 Direction perpendicular to the axis 3     -   10 Openings     -   11 Housing wall     -   12 Means for cooling     -   13 Drive     -   14 Coupling rod     -   15 Diaphragm spring     -   16 Cylinder spring     -   17 Refrigerating device     -   18 Goods     -   19 Gas cushion     -   20 Supply line     -   21 Fluid     -   22 Direction perpendicular to the axis 3 

1-15. (canceled)
 16. A linear compressor having a piston housing and a compressor piston configured for reciprocating movement therein along an axis, the linear compressor having means for guiding the compressor piston in a direction generally perpendicular to the axis and means for buffering kinetic energy associated with the reciprocating movement of the compressor piston, the linear compressor comprising an elastic element made from composite material operatively associated with at least one of the means for guiding and the means for buffering.
 17. The linear compressor according to claim 16 wherein the elastic element is a spring, in particular a diaphragm spring.
 18. The linear compressor according to claim 16 wherein the elastic element is a fiber reinforced element.
 19. The linear compressor according to claim 16 wherein the elastic element includes carbon fibers.
 20. The linear compressor according to claim 16 wherein the elastic element includes glass fibers.
 21. The linear compressor according to claim 16 wherein the elastic element includes aramid fibers.
 22. The linear compressor according to claim 16 wherein the elastic element contains a plastic, in particular a polymer.
 23. The linear compressor according to claim 16 wherein the elastic element is configured for storing and releasing the kinetic energy of the compressor piston during reciprocating movement thereof.
 24. The linear compressor according to claim 16 wherein the elastic element, in particular a spring, is configured for guiding the compressor piston in a direction generally perpendicular to the axis.
 25. The linear compressor according to claim 16 wherein the compressor piston is guided in the piston housing by a housing wall having openings formed therein and a gaseous fluid, in particular a coolant, flowing through the openings.
 26. The linear compressor according to claim 16 wherein the elastic element has a spring constant ranging from about 2000 kg/s² to about 20000 kg/s², in particular between about 3000 kg/s² and about 6000 kg/s².
 27. The linear compressor according to claim 16 wherein the ratio of the transverse rigidity to the axial rigidity of the elastic element is at least about 1:20, in particular at least about 1:50, preferably at least about 1:100.
 28. The linear compressor according to claim 16 wherein the means for guiding and the means for buffering are formed by the elastic element.
 29. A refrigerating device, in particular at least one of a refrigerator and a freezer and an air conditioning unit, the refrigerating device comprising a linear compressor having a piston housing and a compressor piston configured for reciprocating movement therein along an axis, the linear compressor having means for guiding the compressor piston in a direction generally perpendicular to the axis and means for buffering kinetic energy associated with the reciprocating movement of the compressor piston, the refrigerating device comprising an elastic element made from composite material operatively associated with at least one of the means for guiding and the means for buffering.
 30. A method for cooling goods including the steps of providing and operating a refrigerating device, in particular at least one of a refrigerator and a freezer and an air conditioning unit, the refrigerating device comprising a linear compressor having a piston housing and a compressor piston configured for reciprocating movement therein along an axis, the linear compressor having means for guiding the compressor piston in a direction generally perpendicular to the axis and means for buffering kinetic energy associated with the reciprocating movement of the compressor piston, the linear compressor including an elastic element made from composite material operatively associated with at least one of the means for guiding and the means for buffering.
 31. A method for compressing a fluid including the steps of providing and operating a linear compressor having a piston housing and a compressor piston configured for reciprocating movement therein along an axis, the linear compressor having means for guiding the compressor piston in a direction generally perpendicular to the axis and means for buffering kinetic energy associated with the back and forth movement of the compressor piston, and an elastic element made from composite material operatively associated with at least one of the means for guiding and the means for buffering. 